Embodiments of the inventive concept relate to three-dimensional (3D) image sensors and mobile devices including same. More particularly, embodiments of the inventive concept relate to 3D image sensors having increasing demodulation contrast, as well as mobile devices including same.
Certain types of 3D image sensors are capable of measuring the time required for a ranging signal to travel to, be reflected by, and then return from a target object. This measured time is referred to as a time-of-flight (TOF), and may subsequently be used to calculate the distance between the image sensor (or an emitting source) and the target object. The ranging signal used to determine TOF may be a microwave signal, an optical or infrared signal (e.g., an optical pulse), an ultrasonic signal, etc.
Some 3D image sensors essentially determine TOF (and the corresponding distance or ‘depth” separating the 3D image sensor and the target object) using a so-called “depth pixel”. In one configuration the depth pixel may have a 1-tap pixel architecture that sequentially applies gate control signal separated by 0°, 90°, 180°, and 270° of phase difference to the depth pixel with corresponding time lags. The resulting plurality of frame signals may then be used to calculate the depth to the target object.
However, this approach is subject to a number of error inducing incidences. For example, to ensure accuracy of the foregoing calculation, it is necessary to effectively move (or transfer) photo-charge to a sensing node without degradation of demodulation contrast due to an unintended resistance-capacitance (RC) delay.